powerpc64/bpf: do not increment tailcall count when prog is NULL

commit 521bd39d9d28ce54cbfec7f9b89c94ad4fdb8350 upstream.

Do not increment tailcall count, if tailcall did not succeed due to
missing BPF program.

Fixes: ce0761419fae ("powerpc/bpf: Implement support for tail calls")
Cc: stable@vger.kernel.org
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260303181031.390073-2-hbathini@linux.ibm.com
[ Conflict due to missing feature commit 2ed2d8f6fb38 ("powerpc64/bpf:
  Support tailcalls with subprogs") resolved accordingly. ]
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index de99f9b354ab5d67e7ee3976e843ff14d60464fc..94f3f031d039b0e48f37e828dff7735f7a13c2bf 100644 (file)
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -430,27 +430,32 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
 
        /*
         * tail_call_cnt++;
+        * Writeback this updated value only if tailcall succeeds.
         */
        EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), 1));
-       EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), _R1, bpf_jit_stack_tailcallcnt(ctx)));
 
        /* prog = array->ptrs[index]; */
-       EMIT(PPC_RAW_MULI(bpf_to_ppc(TMP_REG_1), b2p_index, 8));
-       EMIT(PPC_RAW_ADD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), b2p_bpf_array));
-       EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), offsetof(struct bpf_array, ptrs)));
+       EMIT(PPC_RAW_MULI(bpf_to_ppc(TMP_REG_2), b2p_index, 8));
+       EMIT(PPC_RAW_ADD(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2), b2p_bpf_array));
+       EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2),
+                       offsetof(struct bpf_array, ptrs)));
 
        /*
         * if (prog == NULL)
         *   goto out;
         */
-       EMIT(PPC_RAW_CMPLDI(bpf_to_ppc(TMP_REG_1), 0));
+       EMIT(PPC_RAW_CMPLDI(bpf_to_ppc(TMP_REG_2), 0));
        PPC_BCC_SHORT(COND_EQ, out);
 
        /* goto *(prog->bpf_func + prologue_size); */
-       EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), offsetof(struct bpf_prog, bpf_func)));
-       EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1),
-                       FUNCTION_DESCR_SIZE + bpf_tailcall_prologue_size));
-       EMIT(PPC_RAW_MTCTR(bpf_to_ppc(TMP_REG_1)));
+       EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2),
+                       offsetof(struct bpf_prog, bpf_func)));
+       EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2),
+                         FUNCTION_DESCR_SIZE + bpf_tailcall_prologue_size));
+       EMIT(PPC_RAW_MTCTR(bpf_to_ppc(TMP_REG_2)));
+
+       /* Writeback updated tailcall count */
+       EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), _R1, bpf_jit_stack_tailcallcnt(ctx)));
 
        /* tear down stack, restore NVRs, ... */
        bpf_jit_emit_common_epilogue(image, ctx);